1. Field of the Invention
This invention relates to hard copy computer display image recording systems and methods and more particularly to a system and method of photographically recording full color video images having spatial and dynamic resolutions far superior to the capabilities of an inexpensive personal computer generating the display.
2. Discussion of the Prior Art
Many small data processing systems are now in widespread use because of their low cost and versatility, and many of these are utilized for generating color displays, in conjunction with which it is often desired to make a hard copy on a transparency or on a positive or negative print. While a relatively small, personal computer, has the data processing power to generate an image of high resolution (say 1000.times.1000) picture elements for a 10".times.10" display it is not economical to use a high cost, high resolution display tube or other device. Instead, the extremely widely used personal computers employ relatively low cost raster scan TV-type. systems, It is necessary to provide color data for three colors concurrently in order to drive the raster scan device in conventional fashion, with three color beams writing concurrently. In order to do this, a display buffer is typically used to store data defining a video image and the data can be read out in raster scan order so as to cause the generation of the image on a color display device. The usual method of making a hard copy is simply to photograph the picture tube of the display device, although impact printers are available which employ different ribbons and require substantial time to provide a printed image. One example of a hard copy photographic recording system is disclosed in application Ser. No. 333,120 filed Dec. 21, 1981 by John K. Cool for "System And Apparatus For Conversion Of Video Signals To Film Images," now U.S. Pat. No. 4,473,849.
It can be seen that the size of the display buffer controls the resolution of the resultant hard copy image. The IBM personal computer provides a good example of this situation. While in conjunction with the CPU of the IBM personal computer an image defined by a large dynamic range of each of three primary colors can be constructed of higher than typically desired resolution, limits on both the spatial and dynamic resolution of the display are imposed by the 16 kilobyte display buffer, which can hold (for 1 bit of monochrome intensity resolution per pixel) an image consisting of 200 vertically positioned horizontal lines having 640 picture elements each. For a color display, a maximum spatial resolution is 320.times.200 with a 2 bit dynamic resolution selecting one of four predetermined colors.
There are numerous applications, however, in which higher resolution color images are desired as evidenced by the commercial success of various systems for generating transparencies and other hard copy for the display of business and commercial data. These systems, however, cost in the tens of thousands of dollars, and require a high rate of use which is incompatible with the important but occasional employment of a personal computer to generate a high resolution image. It is not, on the other hand, feasible to modify the personal computer, which is a standardized and mass produced system. The display portion of one particular personal computer is described in the IBM Personal Computer Technical Reference, pp. 2-45 to 2-63 (1981).